Chloride channels are molecules that are present in hepatocytes and are necessary for multiple liver funtions. Recent studies have identified a family of CIC chloride channels in hepatocytes and suggest that these molecules function in intracellular sites where they are necessary for liver copper transport and vesicular acidification. This project will determine the properties of CIC chloride channels in hepatocytes and define how they participate in liver function and disease. The long-term objectives of this project are to understand how chloride channel abnormalities contribute to Wilson's Disease, cholestatic liver diseases, and other disorders of copper metabolism such as Indian Childhood Cirrhosis so that pharmacological manipulation of chloride channel activity can be used to ameliorate liver injury. The specific aims are: 1. To determine the subcellular localization of the chloride channels CIC-3, CIC-4 and CIC-5 in hepatocytes. To determine specific sequences on the channels responsible for their localization, and the signaling factors which result in changes in this distribution. 2. To determine the channel properties of CIC-3, to understand how its voltage dependence is modulated to allow it to function, and to determine whether functional channel multimers are important for ion conduction. 3. To determine whether CIC chloride channels cooperate with intracellular copper transport ATPases in cellular copper transport. 4. To determine the functional defects and adaptations to loss of hepatic CIC-3 in CIC-3 knock out mice. These aims will be accomplished by the use of immunofluorescence and subcellular fractionation to define the localization of CIC- 3, CIC-4, and CIC-5. Channel function itself will be examined by whole cell and single channel patch clamp. Specific mutations will be produced and exmined for their effects on channel localization and function. The role of CIC-3 in copper transport will be determined by functional assays in yeast and mammalian cells, and its relationship to liver copper homeostasis will be studied in CIC-3 knock out mice by gene expression analysis with DNA arrays and functional response to copper loading of the animals. These experiments will carefully define the role of CIC channels in liver function and will serve as the first step toward the use of chloride channel based therapeutics in liver disease.